lots of great country roads to follow for your trip down. At Buffalo, take Route 5 west all the way to Ripley NY (this is a great drive - very little traffic and curvy, scenic roads), then jump on to the thruway (I-90) west to Rt 8 south, right before Erie (instead of 79 south - it runs parallel). You could go over to Rt 19 south as well, and that is a very nice country drive too. If either route gets too long, just jump onto 79 south to complete the trip.
as for places to stay, there are a few hotels down near the stadium, but may be hard to get a room now. You can stay at one of the hotels on McKnight Rd just north of the city, and drive in for the game on Sunday. I recommend parking downtown at the Theatre Square parking garage on 7th Street (just off Fort Duquesne Blvd), and walking over to the stadium. It will be easier to get in and out of the game, and the tailgaters won't puke on your car.
Supposed to be a great weekend. Hope you are rooting for the Steelers!